This invention relates to an electrophotographic reproducing apparatus and, more particularly, to a document exposure system which eliminates gray borders on a photoreceptor.
A problem common to most commercial copiers is that illumination of a document lying on a transparent platen produces a shadow along the edges of the document. This shadow area is transferred to the photoreceptor in the form of unexposed areas along the edges of the document image. Unless discharged in some manner, these edge "images" are developed and result in an objectionable gray border or edge on the copy sheets.
A number of approaches to solve the foregoing problems of edge or border development have been provided: A typical solution, for copiers with standard imaging lenses, is to position the lens in the optical system so that a slight magnification, usually 1.05.times., is present. This magnification setting moves the gray borders outside of the area of the copy paper. Besides the obvious problem of departing from a desired 1.00.times. magnification, this technique cannot be used for optical systems wherein the magnification cannot be varied from 1.00.times., e.g. when using gradient index lens arrays of the type described in U.S. Pat. Nos. 3,947,106 and 3,977,777 and in strip lenses of the type described in U.S. Pat. No. 3,584,950.
Other solutions to the shadow area problem are disclosed in U.S. Pat. Nos. 3,642,371; 3,788,737 and 4,118,119. These patents disclose and claim various ways of modifying the platen cover to dissipate unwanted edge charge areas. In U.S. Pat. No. 3,642,371, the underside of the platen cover is covered with a diffusely reflective material. U.S. Pat. No. 3,788,737 incorporates an electroluminescent strip in the platen cover which, when excited, provides light to expose edge areas. U.S. Pat. No. 4,118,119 discloses a facetted reflector built into the platen, the reflector set at particular orientations relative to each other.
These solutions are relatively costly and are limited to a specific document and paper width size.
It is therefore one object of the present invention to provide a simple inexpensive device to eliminate gray borders on copy paper.
It is a further object to provide for gray border elimination for copying systems wherein the optical system magnification is restricted to 1.00.times..
It is a still further object to provide an illumination arrangement for eliminating gray borders for a variety of document and copy sheet formats.